1. Field of the Invention
The present invention relates to a capping device for shutting an ink injection port of an ink jet printer.
2. Description of the Related Art
In an ink jet printer of the type where ink pressurized in a pressure chamber is injected onto a recording medium in the form of a number of fine ink droplets to write recorded data, recorded information or the like with the injected ink, it has been found that there is a possibility that a proper writing operation fails to be performed due to an increase of viscosity of the ink caused by vaporization of an ink solvent, drying of the ink, adhesion of dusts, entrapping air bubbles in the ink or the like. To obviate the foregoing malfunction, many proposals have been made to provide a sealing means for the foregoing type of ink jet printer so as to seal an ink injection port with suitable means while the ink jet printer is held in an inoperative state.
One of these proposals is disclosed in an official gazette of Japanese Unexamined Patent Publication (Kokai) No. 1-125239. According to this publication, a sealing device is constructed such that a sleigh, adapted to slidably move by the thrust action of a carriage displaced from the home position, comes near to the lower surface of a printing head with the aid of an inclined guide surface, and a cap molded of an elastic material and placed on the surface of the sleigh is then brought in pressure contact with the lower surface of the printing head so as to seal the injection port of an ink nozzle with the cap.
Another proposal is disclosed in an official gazette of Japanese Examined Publication Patent (Kokoku) No. 2-13910. According to this invention, a sealing device includes two arms as parallel links which are interposed between a frame and a cap so as to allow the cap to come into pressure contact with the lower surface of a printing head. As the cap is displaced in the transverse direction by a carriage, it is also displaced in the direction toward the printing head at a right angle relative to the transverse displacement thereof.
However, with respect to the conventional sealing devices constructed as described above, due to the fact that the quantity of displacement of the cap at a right angle relative to the transverse displacement of the same is restricted by the inclined guide surface and the parallel links, when a distance between the locus of displacement of the carriage and the frame slightly fluctuates due to errors associated with machining operations performed for parts or an assembling operation performed for the parts, or when a distance between a platen and the printing head is adjusted for the purpose of printing data on a paper having a heavy thickness such as an envelope or the like, a distance between the printing head and the cap varies correspondingly. For this reason, a sealing function for the injection port on the nozzle is dependent mainly on the elastic deformation of the cap itself. This does not lead to a significant problem as long as the sealing device has a small sealing surface, but in a case where the printing head includes many nozzles, it becomes very difficult to uniformly seal the whole surface of the printing head with a cap.
Another proposal is disclosed in an official gazette of Japanese Unexamined Patent Publication (Kokai) No. 59-1037862. According to this invention, a sealing device is constructed such that an inverted L-shaped head protective covering is turnably supported at the home position in a one-point supporting fashion so that the head protective cover is turned by a carriage displaced to the home position, causing a cap disposed at one end of the carriage to come into pressure contact with the surface of a printing head.
With the conventional sealing device constructed as described above, since a quantity of turning movement of the head protective covering varies depending on a distance between the cap and the nozzle surface, a reliable sealing function can be assured for a printer adapted to adjust a distance between a platen and a printing head as desired. However, due to the fact that the direction of displacement of the printing head is different from the direction of displacement of the cap, the cap is unnecessarily deformed because of relative displacement between the printing head and the cap. Thus, there arises a problem where the cap is undesirably damaged or broken within a short period of time.
In addition, in order to provide sealing means to close the ink jetting port when the recording device is not in operation, a variety of sealing means have been proposed in the art. In general, the sealing means thus proposed is designed as follows. That is, as disclosed by Japanese Patent Application (OPI) No's 150035/1977 and 238751/1987, a cap member which is so driven as to come in and out of the route of movement of a recording head is arranged at a home position outside a printing region, and, when a carriage is returned to the home position after a recording operation, the cap member held at a retracting position is moved out as soon as the carriage is stopped, thus sealing (or closing) the ink jetting port without slipping on the head surface.
That is, in the conventional ink jet type recording device, the sealing operation is accomplished with a delay time after the recording head returns its home position. Therefore, if the main switch is turned off immediately when the recording head is returned to the home position, then the ink jetting port will not be closed, and accordingly the ink in it may be dried. As a result, the ink jetting port may be clogged up with the ink thus dried. In addition, if the recording device is vibrated for instance when transported, the cap member may be displaced. If this displacement occurs, then the ink may drip, making dirty around the recording device. Furthermore, in the conventional ink jet type recording device, it is necessary to move the cap member to the retracting position for every printing operation. Hence, it takes much time for the conventional ink jet type recording device to start the recording operation.